Does maternal diabetes increase CHD risk? 

Yes, maternal diabetes is a well-established and significant risk factor for congenital heart disease (CHD). Whether a mother has pre-existing Type 1 or Type 2 diabetes, or develops gestational diabetes early in the pregnancy, high blood sugar levels (hyperglycaemia) can interfere with the intricate process of fetal heart formation. Clinical data suggests that infants born to mothers with poorly controlled diabetes have a significantly higher risk of structural heart defects compared to the general population. 

What We will cover in this Article 

• How high blood sugar levels act as a ‘teratogen’ to the developing heart 

• The critical window of heart development in the first trimester 

• Specific types of heart defects linked to maternal diabetes 

• The difference in risk between pre-existing and gestational diabetes 

• Clinical strategies for blood sugar management and risk reduction 

• Statistics on CHD prevalence in diabetic pregnancies 

The Biological Link: Hyperglycaemia and Heart Formation 

The heart is the first organ to form and function in a developing embryo. This process occurs primarily between the third and eighth weeks of pregnancy a time when many women may not yet realise they are pregnant. 

High levels of glucose in the mother’s blood can cross the placenta and disrupt the genetic signals that tell the fetal heart how to fold and divide into chambers. This “glucotoxicity” can lead to oxidative stress in the developing cells, resulting in structural abnormalities such as holes in the heart walls or displaced major blood vessels. 

Types of Heart Defects Associated with Diabetes 

While maternal diabetes can increase the risk of almost any structural heart defect, certain types are more frequently observed in clinical practice. 

Conotruncal Defects 

These are defects affecting the “great vessels” that lead out of the heart. 

• Transposition of the Great Arteries (TGA): Where the two main arteries leaving the heart are swapped. 

• Truncus Arteriosus: Where a single large vessel comes out of the heart instead of two. 

Septal Defects 

These are “holes” in the walls that separate the heart chambers. 

• Ventricular Septal Defect (VSD): A hole between the lower pumping chambers. 

• Atrial Septal Defect (ASD): A hole between the upper receiving chambers. 

Hypertrophic Cardiomyopathy 

In some cases, the heart muscle itself becomes abnormally thick, particularly the septum (the wall between the ventricles). This is often a direct response to high insulin levels in the fetus. 

Comparing Pre-existing vs. Gestational Diabetes 

The timing of high blood sugar is the most critical factor in determining the risk of structural heart defects. 

Type of Diabetes	Timing of High Blood Sugar	CHD Risk Level
Type 1 or Type 2	Present at conception and early 1st trimester	High: Disrupts structural formation
Gestational (GDM)	Usually develops in 2nd or 3rd trimester	Low: Structure is already formed
Undiagnosed Type 2	Present at conception	High: Often missed during the critical window

Reducing the Risk through Management 

The risk of CHD is directly proportional to the mother’s HbA1c levels (a measure of average blood sugar) in the weeks leading up to and during early pregnancy. 

• Pre-conception Care: For women with known diabetes, achieving an HbA1c of less than 6.5% before conceiving significantly lowers the risk to near-normal levels. 

• Folic Acid: High-dose folic acid (5mg) is often prescribed in the UK for diabetic mothers to support healthy neural and cardiac development. 

• Specialist Scanning: Pregnant women with diabetes are routinely offered a fetal echocardiogram (a detailed heart ultrasound) at 20 weeks to check for defects. 

To Summarise 

Maternal diabetes significantly increases the risk of congenital heart disease, particularly if blood sugar levels are high during the first eight weeks of pregnancy. While pre-existing Type 1 and Type 2 diabetes pose the greatest structural risk, early management and pre-conception planning can dramatically reduce these odds. Through specialist monitoring and tight glucose control, the vast majority of women with diabetes can go on to have babies with healthy hearts. 

If you experience severe, sudden, or worsening symptoms such as your newborn turning blue or struggling for every breath, call 999 immediately. 

Authority Snapshot (E-E-A-T Block) 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with experience in general medicine, surgery, and emergency care. Dr. Petrov’s clinical background includes managing diabetic patients and assisting in prenatal diagnostics. His expertise ensures this guide to maternal diabetes and CHD risk follows the 2026 NHS and NICE clinical safety standards. 

Evidence and Clinical Data 

UK clinical guidelines emphasise that the most effective way to prevent CHD in diabetic pregnancies is through strict glycaemic control before pregnancy begins. 

‘Clinical audits show that infants born to mothers with an HbA1c above 10% in the first trimester have a 10% to 15% risk of major congenital anomalies, with heart defects being the most common. Conversely, women who achieve tight control before conception reduce this risk to approximately 1–2%, which is close to the general population average.’ 

 National Institute for Health and Care Excellence (NICE), Diabetes in Pregnancy: Management, 2025 Update. 

[Source: https://www.nice.org.uk/] 

Key Statistics 

• Relative Risk: Women with pre-existing diabetes have a 3 to 5 times higher risk of having a baby with CHD compared to non-diabetic women. 

• Cardiomyopathy: Up to 30% of infants born to mothers with poorly controlled diabetes may show signs of temporary heart muscle thickening at birth. 

• Emergency Advice: If a newborn born to a diabetic mother appears blue, grey, or has severe trouble breathing, call 999 immediately.